$$ 22 3 , 224] Lacaille 281 



those made by him at the Cape formed an important part, 

 led, after an elaborate discussion in which the spheroidal 

 form of the earth was taken into account, to an improved 

 value of the moon's distance, first published in 1761. 



Lacaille also used his observations of fixed stars to 

 improve our knowledge of refraction, and obtained a 

 number of observations of the sun in that part of its orbit 

 which it traverses in our winter months (the summer of 

 the southern hemisphere), and in which it is therefore 

 too near the horizon to be observed satisfactorily in 

 Europe. 



The results of this one of the most fruitful scientific 

 expeditions ever undertaken were published in separate 

 memoirs or embodied in various books published after his 

 return to Paris. 



224. In 1757, under the title Astronomiae Fundamenta, 

 appeared a catalogue of 400 of the brightest stars, observed 

 and reduced with the most scrupulous care, so that, not- 

 withstanding the poverty of Lacaille's instrumental outfit, 

 the catalogue was far superior to any of its predecessors, 

 and was only surpassed by Bradley's observations as they 

 were gradually published. It is characteristic of Lacaille's 

 unselfish nature that he did not have the Fundamenta sold 

 in the ordinary way, but distributed copies gratuitously to 

 those interested in the subject, and earned the money 

 necessary to pay the expenses of publication by calculating 

 some astronomical almanacks. 



Another catalogue, of rather more than 500 stars situated 

 in the zodiac, was published posthumously. 



In the following year (1758) he published an excellent 

 set of Solar Tables, based on an immense series of observa- 

 tions and calculations. These were remarkable as the first 

 in which planetary perturbations were taken into account. 



Among Lacaille's minor contributions to astronomy may 

 be mentioned : improved methods of calculating cometary 

 orbits and the actual calculation of the orbits of a large 

 number of recorded comets, the calculation of all eclipses 

 visible in Europe since the year i^ a warning that the 

 transit of Venus would be capable of far less accurate 

 observation than Halley had expected ( 202), observations 

 of the actual transit of 1761 (227), and a number of 



